Putting it bluntly, yes it is. It has been put there explicitly for the purpose of discouraging what the establishment calls 'fringe' candidates and publicity seekers like Louise Hodges ( Page 3 girl from the Sunday Sport has stood in by-elections).

Although, of course, it has the rather convenient side effect , for them, of making it more expensive and difficult for serious and, in some cases, more representative of ordinary people's opinions , alternative parties like the BNP/National Front/Green Party etc from standing.